1. Technical Field
The present disclosure relates to a light-trapping sheet for allowing light-trapping utilizing diffraction, and to a light-receiving device and a light-emitting device using the same.
2. Description of the Related Art
Where light is propagated between two light-propagating media of different refractive indices, since there is transmission and reflection of light at the interface, it is typically difficult to transfer, with a high efficiency, light from one light-propagating medium to the other light-propagating medium and maintain this state. A conventional grating coupling method shown in “Optical Integrated Circuits”, p 94, p 243, Hiroshi Nishihara, et al. Ohmsha Ltd., for example, can be mentioned as a technique for taking light into a transparent sheet from an environmental medium such as the air. FIGS. 27A and 27B are diagrams illustrating the principle of the grating coupling method, showing a cross-sectional view and a plan view of a light-transmitting layer 20 with a linear grating of a pitch Λ provided on a surface thereof. As shown in FIG. 27A, if light 23a of a wavelength λ is allowed to enter the grating at a particular angle of incidence θ, it can be coupled to guided light 23B propagating inside the light-transmitting layer 20.